Induction motor



Sept. 8, 1931. 0. J. STEWART'ET AL I 1,822,679

INDUCTION MOTOR Filed March 19, 1931 2 Sheets-Sheet l INVENTOR Duncan(IS am;

BYEd

tewar j/Z 0/ am 12L ATTORNEYS Sept. 8 1931. .01.}. STEWART 121' AL1,822,679

INDUCTION MOTOR Filed March 19, 19:51 a Sheets-Sheet 2 ENVENTOR Duncan JStewart g Edgarfl. LZ/Ua ATTORNEYS Patented i i N TE 'STAIES PATENTOFFICE- DUNCAN EW T LIMA. on nocxronn, mmois, assreiions :ro

' nowmn ngcomamor. aocnonn, .1.1

i This invention relates to fractional horse power induction motors 'inwhich shifting of the magnetic field is produced by the action ofshading coils, and more particularly the invention relates. to ashadlng'r ng motor having a two pole stator of the so-called core type,that is, with the energizing winding e nclosing the entire section ofthe magnet c c1r-' cuit through the poles.

v The primary object of the invention 18 to improve the operatingcharacteristics of motors of the above class and thus produce a motorwhich is capable ofde'veloping substan-.

tially reater torque and power and has a much igher efiiciency' thanprior motors of corresponding size.

ore specifically stated, the invention aims to provide'a novel statorconstructed to produce' a highly efie'ctive magnetic field byreason ofthe intensities and phase displacement of its shaded and unshaded fieldcomponents and the manner of their distribution around a squirrel cagerotor, the structure of which is coordinated with and adapted to that ofthe stator so that the full efiect of the rotating field may be utilizedin producing motor action.

A further object is to'provide a motor of the above class having on eachof its poles a plurality of shading fings'of different sizes arranged ina novel and advantageous manner. ,t, r

. Still anothei'ibbject'is to provide a shading ring of .a newand-improved construction.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawings, in which:

Fig. 4 is an enlarged perspectiveview showing the parts of one ofth'eg'shadingf rings.

'two elongated side portions or le Qof substantiallyequal width (8/; i hpmnucrron MOTOR I I I .applicatitn med-Irma 19, 1031. serial no. s2a,2o.

- Fig. 5 is an enlarged perspective View of the rotor partially brokenaway.

Fig. 6 is an actual size side -elevational view 1 v of the statorincluding a diagrammatic representation of magnetic circuits threaded bthevariouscomponents of the magnetic fiel Fig. 7 is a view similar toFig. 6 showing a. difierent arrangement of shading rings and 'the rotorin cross-section. v

Fig. 8 is a view similar toFig. 1 showing a modified form of themotor.

Fig. 9 is a view similar to Fig. 6 showing a tion.

While the invention is susceptible of various modifications andalternative constructions,'1we have shown in the drawings and willherein describe in detail the preferred em bodiment, but it is to beunderstood that we 410 not thereby'intend to limit the invention 0another modification of the stator constructo the specific formdisclosed, but intend to cover all modifications and alternative con-'structions falling within the spirit and scope of the invention asexpressed in the appended claims. I a '7';

' The core type stator or field member ofthe motor shown in the drawingsby way of i1- lustration is com osed of a stack of laminations 10 stampefrom sheets of magnetic 1 iron and having overall dimensions 0f2 incheswide and inches long for a motoroi the preferred size shown in Fig. 6.Each lamination is generally rectangular in form having 11 a'ndl2relatively'shorter end portions" 1-3 ofsu stanti'all the same width asthe side portions. .Pre erably the number and-thickness. of the Figure 1is a P rspective view. of a .niotor, lammatm-ns 113 Such that'thelr sldePort-1011311 r Y embodying the featuresof thepresentinven form acore ofsubstantially square cross sec} 0 .on an insulating' "spool..

, To ,facilitate ,assembly of the core within the'spool, each laminationis out along a sin- 'gle line 15 which intersects and'constitutes anextension of the inner edge of the side portion 11. This enables theadjacent portions of the lamination to be flexedlaterally as Y 'shown inFig. 3, after which the side portion 10! tion orhaving a thickness ofinches. This corejs surrounded by a coil 14 of wire wound I ends,

of the stator laminations are apertured to provide a circular opening17- for receiving a cylindrical rotor 18. The longitudinally alinedportions of the stator leg 12 on opposite sides of the opening 17constitute two magnetic poles with straight parallel side -surfaces 19and opposed concave end faces. For-purposes which will later appear, theside portions or tips of the poles are extended toward each other aroundthe rotor to form a magnetic path between the tips of the oppositepoles. In the motor shown in Fig. 1, the pole extensions are formedintegral with each other so that the tips of-the poles proper are joinedby segments .20 of solid laminated iron. In the rotor illustrated inFig. 8, the laminations forming the extensions are integral at one endonly with the laminations of the pole roper. In both forms,-the innersurfaces of the extensions constitute concontinuations of the pole facesroper, so that the rotor surface is enclosed by a substantiallyuninterrupted iron surface having a width measured axially of the rotorequal to the thickness of the stator. The structural characteristics andfunctions of these pole extensions will be more fully described later.

9 The construction of the rotor 18 has an important bearing upon thetorque and power output of the present Inotor.

It is of the squirrel cage type with its inductor bars constructed andarranged to provide an effective iron section which is relatively largeconsidering the small size of the rotor and which may be worked at ahigh flux density around the entire rotor circumference. In

' practice the rotor is made about three-quarthe notches of the otherdisks to form a plurality of parallel grooves in which are disposedinductor bars 24 electrically connected at their opposite ends by copperdisks 25 which may be of the same shape as the iron ness being about and0.04 inches respectlvely, giving an area of 0.005 square inches whlch isapproximately that of standard N0.

12 wire of circular cross-section.

The most advantageous size of the inductor bars will vary with thenumber of bars employed, the size of the rotor, and the -motorcharacteristics to be obtained. For rotors of the size shown in thedrawings the combined cross-sectional -area of the bars should beapproximately 1 square inches, so that approximately one-sixth of thecross-sectional area of the rotor is comprised of copper.

In order to'minimize radial vibration of the rotor and the noiseincident thereto, the shaft 22 is supported in two rugged bearings.disposed in axial alinement immediately adjacent opposite ends of therotor. The bearings are .formed at the center of two bracket plates 26of non-magnetic material whose opposite ends are bent so as to lie flatagainst the sides of the stator at opposite ends of the stator legs 12to which the plates are securely bolted.

The width of the gap around the rotor is determined by numerous factorsincluding the rotor reactance, the tendency of the rotor to vibrate, andmanufacturing difliculties in obtainin a gap of narrow and uniformwidth. %n the present instance, the radial width ofthe gap between therotor surface and the pole faces is 0.011 of an inch.

The rotating magnetic field for producing rotational movement of therotor is produced by the well-known shading ring method. That is tosay,one side portion of each pole is enclosed by a short-circuited conductorin which currents are induced by the transformer action of the mainfield flux threading the ring when the coil 14 is energized byalternating current. The effect of the currents induced in the rings isto' oppose the change in the flux in the enclosed portion of each pole,withthe result that the flux in the unshaded pole area rises to itsmaximum value before the flux in the shaded area. Owing to thisso-called time lag or phase displacement, the magnetic field is said toshift across the pole faces producing motor action on the rotor as iswell understood in the art.

In the drawings two shalding ring arrangements are disclosed, therebeing'one ring 27 per pole in the motor shown in Fig. 6 and a similarring and also an additional ring 28 on each pole in-the motor shown inFigs. 1

' length of copper wire 29 bent to a "thereby defining two straightparallel legs or 7. In order to reduce manufacturing costs] and the-size of the motor as a-whole section 38 p're each'shading ringhereinshown corn rises a p side'portions, one of which is insertedthrough a-ho'le 30 formed in the stator laminations ad'acent the rotorrecess 17.

surface of the'wire 29. Thus a large contact area is provided betweenthe separable parts of the which are suitably secured to During thesoldering operation, the cone legs'of the U-shaped wire are of a lengthgreater than the thicknessof the stator so that their ends projectbeyond the terminal stator lamination.v These ends are connected by acopper bar 31 preferably of That metal'stock so as to lie flat againstthe stator surface. .At' opposite ends, the bar 31' isvfo'rmed withconcave surfaces which fit around and conform closely to the convexgather by t e application ofsolder attheir oints cave ends of the bar 31may be held convenlaminationSso as to p oyide a non-ma iently in'abutting relation with respect to the sides of the'legs'ofthe wire 29 byinsert ing the bar between the projecting ends of the wire and forcingthese toward each other.

. With thearts thus held in clamping engagement, sol er is applied tothe joints and ad acent surfaces of the bar and member 29.

Preferably slots 32 are cut in the stator et1c gap between the unshadedand shade pole sections, and between the sin 1e and double shadedsections in the form the invention shown in Fig. 1. Thus the face ofeachpole of the motorshown'inFig. 6 is divided mm an unshaded area '33anda shaded area 34.

In the motorshown in Figs. 1 and 7 having, two'jshading rings'oneachpole, the slots 32 form an unshaded area 35, an adjacent single shadedarea 36, and a double shaded area 37 on the side of the pole oppositethe unshaded area. -The effect of such a gap is to increase thereluctance of'the local magnetic circuit defined by the stator'ironaround and. im-

inediately adjacent the enclosed leg of the -shading ring. To. avoiddecreasing the pole 9 face area appreciably, the gap should be made verynarrow, at leastat and adjacent the rotor recess.

Wherethereis only one shading ring on each pole, as in the form of theinvention shown in Fig. 6, the ring should be located closely adjacentthe rotor recess and prefer ably enclose not more than one-halfiof thetotal pole sectional area.

The torque of the motor may be materially improved throu h the use of aplurality of shading rings 0 different sizes on each pole and enclosingdifferent proportions of the total pole section. Thus the ring 27preferably encloses one-third of the total'pole section. The larger ring28 encloses'this same areas are disposed on the shading section ofthePole and also'an additional rably approximately equal in cross-sectionalarea to and at least not matenally greater than the section 39 enclosedb}: the smaller 'rin With the arrangement s own, the unsha ed section40, the section '38 shaded only by the ring 27 and the section 39-enclosed by both rings are of approximately equal areas. These sectionsare separated by the gaps 32, thus dividing the pole face'into theunshaded, singleshaded and double shaded areas 35, 36 and 37respectlvely. The corres ondingly. shaded v 'a'metrlcally .oppositesides of thevrotor.

When'a plurality of shading rings arelemployed ion ,eacli-; pole, theyare; preferably mounted on. the stator so that their corresponding sides'will be disposed in closely spaced-butdiflerent planes. Sucharrangement enables all of the le s of the rings to lie flatjagainstthe-pole sur aces and the length ereiore the. resistances .of the r'minimum. Materi of sectional area may therefore v roviding for thedesired low resistance-of, errings. Furthermore,., he rings.thus"arrangeddonot project. an appreciable distance beyond theoutermost points ofthe stator leg 12 so that the overall width of thestator and the length of the magnetic circuit therethrough .areminimized. In addition the stator efiectuallyholds the rings againstlateral displacement thereby maintaining them in properly insulatedrelation even though they are spaced close together. The

maintenance of such relation is important because electrical contactbetween the rings would establish auxiliary circuits in which L.

ase as far as ssible from the field threa ingthe unsha ed section of thepole. As shown diagrammatically in 6, the field threading the shadedpole areas may be considered as the resultant of a main field component,the mean path of-which is represented by the line 41,and a lag componentdue to the current induced in the ring. The latter component isaffected-by the reluctance of magnetic circuits the mean paths of whichare indicated by the lines' 12,

(Fig.6). g v It will be I apparent that an increase in by decreasing thephase displacement of the of the larger rin resultant flux through theshaded pole section. At the same time, such an increase in ringresistance decreases the opposition of the shading ring andthereforeincreases the value of the component 41. Thus, with an increasein ring resistance, the shaded field is less effective from thestandpoint of phase displacement, but it is of greater magnitude due tothe higher value of the component 41. Conversely, a decrease in ringresistance will increase the lag of the shaded field but will decreaseits magnitude.

For best results" a compromise is established between these twoopposingfactors and a shading ring resistance is employedwhich results in theproduction of optimum power and torque. In motors of the size shown inFig. 6 and having one shading ring on each pole, the ring resistanceshould be approximatelybetween 1 and 2 x 10" ohms. Rings formed fromNos. 8, 9, 10 or 11 standard copper wire of circular cross-section wouldhave resistances within this range and the currents induced in suchrings in the motor herein disclosed would be within a range of fromapproximately 100 to 200 amperes.

Where two shading rings are provided on each pole, the resistance of thesmaller should be within the range above specified .but a widervariation is allowable in the resistance The latter may be made of anysize wire from No. 8 to No. 14.

For motors of sizes different from that shown inFigs. .6, 7 and 9, thecross-sectional area of the shading ring wire required to give bestmagnetic performance should be larger in the case of a smaller motor andsmaller for larger motors in order to maintain the shading ring currentapproximately constant. This requirement imposes a fixed limitation uponthe size of motor which can be constructed. This is because the shadingring losses increase with the size of the motor at a more rapid ratethan the surface areas for dissipating the heat due to such losses.

From the foregoing considerations, it will be apparent that the mosteffective shaded field which can be produced'in a motor of,

the present type is inherently weaker than the unshaded field andtherefore requires a shaded flux will be worked at relatively highdensity by unshaded flux.

The utilization of a lar er unshaded field .in the rotor iron is accompished in the pres- 33 (Fig. 6) and 35 (Fig. 7) by means of magneticextensions of the unshaded tips of the poles proper. These extensionsclosel follow the rotor contour so that the un'sliaded flux may enterthe rotor iron along the entire length of the extension to a pointbeyond the midline 43. Thus, the rotor iron exposed to these extensionsis utilized at high density when the unshaded pole extensions aresubstantially saturated.

In the present instance, the segments 20 formmagnetic paths of lowreluctance for effecting proper distribution of the unshaded" tip of thepoles proper so as to present a con- In tinuous iron surface on theirinner sides. all forms of the motor shown in the drawings, theextensions project around the rotor surface toward the opposite pole toa point at least closely adjacent the center line 43 so that asubstantial amount of unshaded flux enters the rotor iron beyond suchline.

Preferably the 'magnetic extensions project uninterruptedlyabeyond theline 43 thereby eifecting a still greater enlargement of the unshadedpole area from which the unshaded flux may enter the rotor iron. Asshown in Figs. 1 to 7, the uninterrupted extension may completely closethe space between the two poles and be formed integral with the shadedtip of the opposite pole. Or, where the stator laminations are made intwo parts brought together at butt'joints, one of the joints in thefield member may be adjacent the line' While provision of an integralconnection between the shaded tip of one pole and the projected end ofthe unshaded pole extension isconducive -to the leakage of some fluxaround the rotor which might otherwise thread the same, it simplifiesmanufacture and enables the rotor recess to be accurately defined andthe rotor air gap to be reduced to a minimum width and maintaineduniform around the entire rotor circumference. If desired, the fluxleakage above mentioned may be reduced by introducing a reluctance suchas a narrow air gap 44 (see Fig. 8) in the segment 20 between the line43 and the shaded tip, preferably nearer the latter. For

best results this gap should be very narrow, e. g. approximately 0.013inches but maybe increased to 0.030 inches without seriously reducingthe power. other equivalent restriction does not interfere with thedistribution of the unshaded flux to the rotor iron atpoints beyond thecenter line 43. By making the reluctance in the form of a hole 45 (Fig.9), the rigidity of the stator structure definin therotor recess may bepreserved and the ux leakauge d at the same time reduced. The hole shoSuch a reluctance or pole Y In a dition to the function of causing sh ft1? sting of the magnetic field, the shadingrings vwhen made ofrelatively low resistance erformthe function of opposing leakage or theunshaded flux frornrthe unshaded tip extensions directly to the shadedtip of theo 'posite pole thereby causing Substantially a of theavailable unshaded 'fiux' threadm the 1 pole extension to be divertedthrough t e rotor and soy utilized in the production of motor r'natelyof the rangeabovespecified for obthe pole section enclosed by the ring.

taining most effective shading action will create the desired forceopposing leakage-of the unshaded flux, due regard being given to thesize of the motorand the proportion of It is also to be observed in thisconnection 'I that when two shading rings areemployed on each pole andarranged as shown in Figs. 1 and 6for the urpose ofproducinga uniforml'yprogressive shifting of the field across thepole faces, the longer rmgs28 enclose the side portions of the holes through whichthe unshaded fluxtends to leak as above set forth. The currents induced in these longerrings augment'the magneto-motive force produced by the small ringsandtherefore perform the additional function of causing more effectiveposition to the undesirable flux leakage. he radial width of theunshaded pole extensions at the center line'43 or at the narrowest pointalong their length may vary somewhat without'appreciably impairin themotor output. Segments g inches wi e or approximately one-seventh of thewidth of the poles have proven most effective in producing properdistributionof the unshaded flux while maintaining, high efiiciency ofthe motor. The shape of the outer surfaces of the seg nients 20 1snot-ofmaterial importance'so long as theinner surfaces closely follow thecontour of the rotor, that is, are spaced therefrom approximately thesame distance as the faces of the poles proper. Herein, the segmeritsare formed with convex outer surfaces which enables the overall widthofthe motor to'bereduced without decreasing the ower output. Thus, thepoles are made 0 substantially the same width as the winding core 11with the segments20 bulging out- 'war'dly beyond the sides 19. of thepoles so as to occupy the same spaces ilaterally of the poles as areoccu ied by the shading rin A- double reduct1onin the width of t e belocated between the line 43 and:- the shaded tions 40 resulting from theaddition of the 'thetime. phase relation which, it W111 be remotor isthus effected with such construction which" also permits smaller wiretobe used for theshading-rin' It will be apparentgzm the foregoing thatextension of theunshadedpole areas around the mm is advantageous in thepresent motor because therotor em loyed is of small diameter and asubstantial propore tionof its periphergis obstructed'by'therelatively'large num er of non-magnetic inductor bars. With suchextensions, larger segments" of the rotor surface and therefore lar erareas of effective iron are'enclosed an thereby made availablefor entryof the predominating unshaded field and no parts 0 Of the rotorjironare. unduly saturated. In the case of 'the motor having-two shadingrings on each pole, the magnetic extensions compensate for the decreasein the pole'seclar' er ring. Thus, it will be seen from Fig. 7 t at theeffective iron area of the rotor teeth 23 enclosed by each unshaded areaand its extension up to the center line 43 is ap roxlmately equal to andtherefore is capa le of carrying substantially all of the flux capableof being delivered by the unshaded section of the pole. In the case ofmotors having'only one shading ring on each pole, the unshaded areas 33of the poles pro r enclose a larger number of the rotor teet than in thecase of the motor shown in Fig. .7; nevertheless the unshaded 'poleextensions are required in order that the rotor iron may utilizethe'larger amount of flux threading the unshaded section which, it willbe ohserved, is ofsubstantially greater cross-sectional area than in thecase of the motorhaving two rings on each pole.

Ina'smuchas the segments 20 cause a substantialamount of unshaded fluxto enter the rotor near or beyondthe center line 43, the

effect is to shift the mean line 46 of the unshaded field nearer to theline 43 and thereby increase the space displacement of the unshadedfield re ative to the shaded field. In this way, the space relation ofthe shaded and unshaded components of the rotating magnetic field morenearly. corresponds to in the capacity of the pole extension to maintainthe roper unshaded flux density at points ad acent or beyond the midline43 where such .flux'can be tilized eificiently.

Such a decrease would occur for example where an air gap of substantialwidth such as has been commonly employed heretofore in motors of thepresent type is located midway between the pole tips. I

On the other hand, if the interruption is in the form of a butt joint oris in the form of an extremely small ga on the order of a fewthousandths of an web, the decrease of the flux is in such case so smallas not to affect the output of the motor materially. With the gap of awidth not exceeding that between the rotor and pole faces and locatedalong the line 43, the power of the motor is not materially reduced. Amarked reduction results if the width of the gap located adj acent theline 43 is increased to g, of an inch. The detrimental effect of ahigh-reluctance section in the segments 20 is more noticeable whensuchsection is offset from the line 43 in the direction of the unshadedpole; in fact any high reluctance section in this part of the segment isdetrimental from the standpoint of power and torque because such asection reduces the effectiveness of the rotor iron adjacent and beyondthe line 43 in utilizing the available unshaded flux.

Another function of the magnetic extensions of the unshaded pole tips isto decrease the reluctance of the magnetic circuits 42. It will beobserved from Fig. 6, that substantiall the entire length of thesegments 20 are included in the circuits 42 so that if the segments 20were interrupted between the line 43 and the unshaded pole tips byappreciable air gaps or other reluctance sections, the value of themagnetic field due to the induced shading ring currents would be reducedac cordingly.

In order that extensions of the unshaded pole tips may function in themanner above described, the coil 14 is constructed to have sufficientmagneto-motive force to substantially saturatethe available rotor ironand 1 the winding core 11, and other parts of the stator are ofsuflicient size to carry the flux thus required. y

In the appended claims the expression magnetic extensions for causingeffective distribution of unshaded flux to the rotor iron over anenlarged range extending beyond the midpointbetweenthepolescontemplatesand includes the following equivalent structures; solid laminatedextensions such as the segments 20 continuous or interrupted near theshaded pole substantially as shown, or the segments 20 having betweenthe unshaded pole tips and the median plane between the poles an air gapor other equivalent restriction producing a magnetic effect less than aradial air gap of an inch wide located at said median plane.

This application forms a continuation in part of our former applicationSerial No.

407,819, filed November 18, 1929.

We claim as our invention:

1. In an induction motor, the combination of a field member having aplurality of poles, a rotor exposed to the faces of said oles, and aplurality of shading rings of di erent sizes mounted on each of saidpoles adjacent said rotor with all of the rings on each pole enclosing acommon pole section and the larger rings enclosing additional sections,the corresponding portions of the rings on each pole being disposed indifferent closely spaced transverse planes through the pole.

2. A small induction motor having a core type stator. providing twoopposed poles, a cylindrical rotor having an iron core and inductor barsspaced around the core periphery, two relatively small shading ringsenclosing side portions of said poles on diametrically opposite sides ofsaid rotor, and two larger shading rings one on each pole enclosing thesame section as the smaller ring and also an additional sectionapproximately equal in area to but not materially greater than thesection enclosed by said smaller ring.

3. An alternating current induction motor combining a stator of the coretype providing two poles having opposed concave faces, a rotor of thesquirrel cage type between said poles, shading coils enclosing sideportions of said poles on diametrically op osite sides of said rotor anddividing said aces into a section from which unshaded flux enters therotor and a shaded section from which a lagging flux enters the rotor,and magnetic connections between said poles having their op posite endsintegral with the shaded and unshaded side tips of the opposite polesand providing inner iron surfaces closely following the rotor contourand enclosing all of the rotor iron between the poles, said rings beingof such low resistance that the currents induced therein produce amagneto-motive force strongly opposing the leakage of fiux directlybetween said poles whereby to cause substantially all of the unshadedflux thread ing said connections to be utilized in the rotor.

4. An alternating current induction motor comprising a stator of thecore type composed of a stack of iron laminations and provlding twopoles having opposed concave faces, a cylindrical squirrel cage rotordis osed between said poles,-shortc1rcuited sha ing coils enclosing sideportions of said poles on diametrically opposite sides of sald rotor anddividing said forces into a section from which unshaded magnetic fluxenters the rotor iron and a section threaded by a lagging flux, andmeansenlarging the range of distribution of said unshaded flux to therotor iron comprising an extension of each unshaded pole tip followingclosely the rotor surface and adapted to distribute a substantial amountof unshaded flux to the rotor iron beyond the median plane between thepoles, each of said shading coils being of low resistance so that thecurrent induced therein produces a magneto-motive force of sufficientmagnitude to oppose any substantial leakage of unshaded flux directlythrough the extensions to the shaded pole tips whereby to divertsubstantially all of the unshaded flux threading said extensions intothe rotor.

5. An alternating current induction motor combining a laminated statorof the core type providing two poles having opposed concave faces, acylindrical rotor of the squirrel-cage type disposed between said poles,short-circuited shading coils of low resistance enclosing side portionsof said poles on diametrically opposite sides of said rotor so as todivide each of said faces into a section from which unshaded magneticflux enters the rotor iron and a section threaded by a lagging flux, andmeans enlarging the range of distribution of said unshaded flux to therotor iron comprising magnetic extensions of each unshaded pole sectionfollowing closely the contour of the rotor, said rings of low resistanceand said magnetic extensions cooperating to cause effective distributionof unshaded fiux to the rotor beyond the median plane between the poles.

6. An alternating current induction motor combining a stator of the coretype providing two poles having opposed concave faces, a cylindricalrotor of the squirrel-cage type disposed between said poles,short-circuited shading coils of low resistal'r'e enclosing sideportions of said poles on diametrically opposite sides of said rotor anddividing each of said faces into a section from which unshaded magneticflux threads the rotor iron and a section threaded by a lagging flux,and means cooperating with said coils of low resistance to causeeffective distribution of unshaded flux to the rotor iron between saidunshaded face sections of the poles and points beyond the median planebetween the poles comprising a solid laminated extension of eachunshaded pole tip projecting around the rotor toward the shaded tip ofthe opposite pole and having an inner iron surface closely following therotor contour, each extension between the said median plane and theunshaded pole tip having no restriction therein greater in magneticeffect than a radial air gap of an inch wide located at said medianplane.

7. An alternating current induction motor combining a stator of the coretype providing two poles having opposed concave faces, a rotor of thesquirrel cage type between said poles, shading coils enclosingside-portions of said poles on diametrically opposite sides of saidrotor and dividing said faces into a section from which unshaded fluxenters the rotor and a shaded section fromwhich a lagging flux entersthe rotor, and extensions of the unshaded tips of said poles closelyfollowing the rotor contour and constructed to distribute a substantialamount of unshaded flux to the rotor iron beyond the median planebetween the poles, said stator having an overall dimension'ofapproximately 2 inches wide and 2% inches long with legs approximatelyinches wide and f}; inches thick, and said coils having a resistance ofapproximately 1 to 2 x 10' ohms.

8. An alternating current induction motor combining a stator of the.core type providing two poles having opposed concave faces, a rotor ofthe squirrel cage type between said poles, shading coils enclosing sideportions of said poles on diametrically opposite sides of said rotor anddividing said faces into a section from which unshaded flux enters therotor and. a shaded section from which a lagging flux enters the rotor,and extensions of the unshaded tips of said poles closely following therotor contour and constructed to distribute a substantial amount ofunshaded flux to the rot-oriron beyond the median piano between thepoles, each of said coils having a resistance such that the currentinduced therein is within a range of from approximately 100 to 209ampcres.

9. [in alternating current induction motor com -iining a stator of thecore type providing two poles having opposed concave faces, acylindrical rotor of the squirrel-cage type disposed between said poles,short-'circuitcd shading coils enclosing side portions of said poles ondiametrically opposite sides of said rotor and dividing each of saidfaces into a section from which unshaded magnetic flux threads the rotoriron and a section threaded by a lagging flux, an extension of eachunshaded pole tip closely following the rotor contour and projecting toa point adjacent the shaded tip of the opposite pole, thecurrentsiuduced in said rings producing a magneto-motive force tendingto oppose the leakage of unsh aded flux around said rotor whereby todivert such flux into the rotor, and a second shading ring on each poleenclosing the same section as said first ring and-also an additionalsection and serving to produce a progressive shifting of the magneticfield across each pole face and also to create additional opposition tothe leakage of unshaded flux from said extensions to the shaded poletips.

10. An alternating current induction motor combining a stator of thecore type providing two poles having opposed concave faces, anenergizing winding on the stator, a cylindrical rotor of thesquirrel-cage type disposed between said poles, short-circuited shadingcoils enclosing side portions of said poles on diametrically oppositesides of said rotor and dividing each of said faces into a section fromwhich unshaded magnetic flux threads the rotor iron and a sectionthreaded by a lagging flux, each of said unshaded pole sections havin.an extension in the direction of the opposite pole following closelythe contour of the rotor and proportioned so as to cause effect-ivedistribution of unshaded flux to the rotor beyond the median plane, saidstator and winding being constructed so as to be capable of maintainingthe pole faces and the faces of said extensions substantially 1saturated.

11. An alternating current induction motor comprising a'stator of thecore type composed of a stack ofiron laminations and providing two poleshaving opposed concave faces, an energizing winding on the stator, acylindrical squirrel cage rotor disposed between said poles,short-circuited shading coils enclosing side portions of said poles ondiametrically opposite sides of said rotor and dividing said faces intoa section from which unshaded magnetic flux enters the rotor iron and asection threaded by a lagging flux, and means enlarging the range ofdlstribution of said unshaded flux to the rotor iron compris- 2 ingextensions'formed integral with the stator laminations and projectingfrom each unshaded pole ti in closely spaced relation to the rotor anconnected with the opposite shaded pole tip, said stator and windingbeing so constructed as to be capable of maintaining the pole faces andthe faces of said extensions substantially saturated.

12. An alternating current motor combining a cylindrical rotor of thesquirrel cage type having a plurality of copper inductor bars of acombined cross-sectional area equal approximately to one-sixth of thetotal crosssectional area of the rotor, a stator of the core type havingtwo opposed poles embracbracing said rotor, shading rings of lowresistance enclosing side portions of said poles on diametricallyopposite sides of said rotorand dividing each pole into shaded andunshaded sections, and magnetic extensions of the unshaded pole sectionsclosely following the rotor contour and adapted to distribute asubstantial amount of unshaded flux to the rotor iron beyond the medianplane between the poles.

" In testimony whereof we have hereunto afiixed our signatures.

DUNCAN J. STEWART. EDGAR D. LILJA.

